Switching power supply device

Abstract

To provide a switching power supply device complying with an electric shock protection class 2 that is able to effectively prevent noise current flowing in a ground resistor.SOLUTION: A voltage generated in a primary-side main winding 24 (1) becomes a noise source, resulting in generation of a noise current Icom (1) that flows out to a ground line 32 through unstable-potential stray capacitors Cf1 to Cf3 and a noise current Icom (2) that flows out to the ground line 32 through a secondary-side stray capacitor Cy2. An insulating transformer 22 has a secondary-side auxiliary winding 40(2) one end of which is connected to a secondary-side stable potential line 14; and a capacitance forming region 42c of a wiring pattern 42 connected to the other end of the secondary-side auxiliary winding 40(2) and a capacitor forming region 44c of a primary-side stable potential line 12 are disposed opposite to each other to form a wiring-pattern stray capacitor Ch. When a predetermined level of current flows through the wiring-pattern stray capacitor Ch, a magnitude of the current obtained by combining the noise currents Icom (1) and Icom (2) can be restricted to a reference value or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an isolated switching power supply device in which a primary side circuit and a secondary side circuit are connected via an isolation transformer. [Background technology]

[0002] Conventionally, as disclosed in Patent Document 1, for example, there has been a switching regulator in which a noise compensation winding is provided on the secondary side of the transformer to generate a voltage of the same level and opposite polarity as the common mode noise voltage, and a capacitor element is connected between the end of the noise compensation winding where the opposite polarity voltage is generated and the input power line, in order to cancel the effect of the common mode noise current flowing from the primary winding to the secondary winding of the transformer. With this configuration, a cancellation current of the same level as the common mode noise current can be generated and can be caused to flow back to the primary side through the capacitor element, thereby canceling the effect of the common mode noise current. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 1-64986 Summary of the Invention [Problem to be solved by the invention]

[0004] 16 is a device classified as class 2 in electric shock protection defined by IEC standards, JIS standards, etc. First, the configuration of the internal circuit of the switching power supply 10 will be described. The switching power supply 10 is configured to convert an input voltage Vi input between a primary power supply line 12a and a primary ground line 12b, which are made up of a pair of wiring patterns, into a predetermined output voltage Vo, and generate it between a secondary power supply line 14a and a secondary ground line 14b, which are also made up of a pair of wiring patterns.

[0005] A primary side interphase capacitor element 16 is connected between the primary side power supply line 12a and the primary side ground line 12b, and the two lines 12a, 12b are substantially short-circuited by the primary side interphase capacitor element 16 in a frequency band equal to or higher than the switching frequency Fsw, forming a potentially stable primary side stable potential line 12. Similarly, a secondary side interphase capacitor element 18 is connected between the secondary side power supply line 14a and the secondary side ground line 14b, and the two lines 14a, 14b are substantially short-circuited by the secondary side interphase capacitor element 18 in a frequency band equal to or higher than the switching frequency Fsw, forming a potentially stable secondary side stable potential line 14.

[0006] An inverter circuit 20 is connected to the primary power supply line 12a and the primary ground line 12b. The inverter circuit 20 has an isolation transformer 22 (primary main winding 24(1), secondary main winding 24(2)) and a switching element 26. The primary main winding 24(1) and the switching element 26 are connected in series, and the switching element 26 is switched at a switching frequency Fsw to generate a voltage that is an intermittent version of the input voltage Vi across the primary main winding 24(1).

[0007] A rectifier circuit 28 that rectifies the voltage generated in the secondary main winding 24(2) of the isolation transformer 22 to generate a rectified voltage is connected to the secondary main winding 24(2), and a smoothing circuit 30 that smoothes the rectified voltage to generate an output voltage Vo is further connected to the output terminal of the rectifier circuit 28. The switching power supply device 10 is a so-called flyback converter, in which the rectifier circuit 28 is composed of one diode 28a, and the smoothing circuit 30 is composed of the secondary interphase capacitor element 18, and the output voltage Vo is generated across the secondary interphase capacitor element 18.

[0008] To explain the actual usage state of the switching power supply device 10, the switching power supply device 10 is connected to an input power source 34 grounded to a ground line 32 via a ground resistor Rs, and an input voltage Vi is input to a primary side stable potential line 12 (12a, 12b). In addition, the secondary side stable potential line 14 (14a, 14b) is connected to an external load 36, and an output voltage Vo is output to the external load 36.

[0009] At this time, the primary side stable potential line 12 and the ground line 32 are connected by a primary side stray capacitance Cy1, and the secondary side stable potential line 14 and the ground line 32 are connected by a secondary side stray capacitance Cy2. In addition, an inter-winding stray capacitance Ct is formed between the primary side main winding 24(1) and the secondary side main winding 24(2).

[0010] Furthermore, the wiring patterns at a plurality of locations in the inverter circuit 20, the rectifier circuit 28, and the smoothing circuit 30 where a pulse voltage having an amplitude of the switching frequency Fsw is generated are connected to the ground line 32 by unstable potential floating capacitance. Specifically, the connection point between the primary main winding 24(1) and the switching element 26 is connected to the ground line 32 by unstable potential floating capacitance Cf1, and the connection point between the secondary main winding 24(2) and the rectifier circuit 28(28a) is connected to the ground line 32 by unstable potential floating capacitance Cf2.

[0011] The capacitance values ​​of the above stray capacitances Cy1, Cy2, Ct, Cf1, and Cf2 are usually small values ​​of several tens of pF or less, and are stray capacitances that should be considered as the main paths through which switching noise flows. Note that there are many other stray capacitances between the switching power supply device 10 and the ground line 32. However, the voltages across the stray capacitances other than Cy1, Cy2, Ct, Cf1, and Cf2 do not change AC-wise (or the change is very small), so they can be ignored with regard to the problem of input feedback noise, which will be described later.

[0012] Next, the problems with the switching power supply 10 will be described. Because the switching power supply 10 is an electric shock protection class 2, numerous stray capacitances Cy1, Cy2, Ct, Cf1, and Cf2 are formed between the internal circuit and the ground line 32 in actual use, and the voltage generated in the primary main winding 24(1) becomes a noise source, causing noise currents to flow from each stray capacitance to the ground line 32, resulting in a problem of increased input feedback noise. Input feedback noise is noise that flows out from the switching power supply 10 toward the input power supply 34.

[0013] In general, the common mode component of input feedback noise is evaluated based on the magnitude of the noise current Icom that flows through the ground resistance Rs. For example, the noise terminal voltage, which is one of the evaluation items in the EMI standard, is evaluated by inserting a LISN (artificial mains network) with a fixed resistor of several tens of ohms that simulates the ground resistance Rs between the input power supply and the input terminal of the power supply device and the ground line, and evaluating the frequency characteristics (150k to 30MHz) of the voltage generated in the fixed resistor.

[0014] In order to suppress the common mode component of the input feedback noise in the switching power supply device 10, it is important to design it so that the noise current Icom flowing through the ground resistor Rs is small under actual use conditions. However, since it is a device that complies with electric shock protection class 2 and has many stray capacitances Cy1, Cy2, Ct, Cf1, and Cf2, it is not easy to appropriately control and suppress the noise current Icom.

[0015] For example, the technology of Patent Document 1 cancels the current flowing through the stray capacitance Ct between the primary main winding and the secondary main winding of an isolation transformer, and can be said to be a technology that substantially reduces the capacitance value of the stray capacitance Ct to a negligible level. However, even if this technology is applied to the switching power supply device 10, only one of the many stray capacitances Cy1, Cy2, Ct, Cf1, and Cf2 (the stray capacitance Ct) is reduced, and the noise current Icom cannot be effectively reduced.

[0016] The present invention has been made in consideration of the above-mentioned background art, and has an object to provide a switching power supply device that complies with electric shock protection class 2 and is capable of effectively suppressing noise current flowing through a ground resistor. [Means for solving the problem]

[0017] The present invention provides a device which is formed by mounting circuit components on a printed wiring board having a plurality of wiring layers, converts an input voltage input between a primary power supply line and a primary ground line which are formed by a pair of wiring patterns into a predetermined output voltage which is generated between a secondary power supply line and a secondary ground line which are also formed by a pair of wiring patterns, a primary side interphase capacitor element connected between the primary side power supply line and the primary side ground line, for substantially shorting the primary side power supply line and the primary side ground line in a frequency band equal to or higher than a switching frequency, thereby making the two lines into a primary side stable potential line that is stable in terms of potential; a secondary side interphase capacitor element connected between the secondary side power supply line and the secondary side ground line, for substantially shorting the secondary side power supply line and the secondary side ground line in a frequency band equal to or higher than the switching frequency, thereby making the two lines into a secondary side stable potential line that is stable in terms of potential; an inverter circuit including an isolation transformer and a switching element, a primary main winding of the isolation transformer and the switching element being connected in series, and the switching element being switched on and off at the switching frequency to generate a voltage that is an intermittent version of the input voltage across both ends of the primary main winding; a rectifier circuit connected to a secondary main winding of the isolation transformer, the rectifier circuit rectifying a voltage generated in the secondary main winding to generate a rectified voltage; a smoothing circuit including the secondary side interphase capacitor element, smoothing the rectified voltage to generate the output voltage across the secondary side interphase capacitor element; In an actual use state, the input voltage is supplied from an input power supply that is grounded to a ground line via a ground resistance, the primary side stabilized potential line and the ground line are connected by a primary side floating capacitance, the secondary side stabilized potential line and the ground line are connected by a secondary side floating capacitance, inter-winding floating capacitance is formed between the primary side main winding and the secondary side main winding, wiring patterns at locations in the inverter circuit, the rectifier circuit, and the smoothing circuit where a pulse voltage that oscillates at the switching frequency is generated are connected to the ground line by non-stable potential floating capacitance, This is a switching power supply device in which the voltage generated in the primary main winding becomes a noise source, generating a first noise current that flows into the ground line through the non-stable potential floating capacitance and a second noise current that flows into the ground line through the secondary floating capacitance.

[0018] In the case of the invention described in claim 1, the insulating transformer has a secondary side auxiliary winding, one end of which is connected to the secondary side stable potential line, a wiring pattern connected to the other end of the secondary side auxiliary winding has a second main body region and a second capacitance forming region continuous therewith, the primary side stable potential line has a first main body region and a first capacitance forming region continuous therewith, the first and second capacitance forming regions face each other to form a wiring pattern stray capacitance, the wiring pattern stray capacitance is set to a predetermined capacitance value by adjusting the facing area of ​​the first and second capacitance forming regions, and a current according to the capacitance value flows through the wiring pattern stray capacitance in the actual use state, thereby suppressing the magnitude of the combined current of the first noise current and the second noise current to a reference value or less. In this case, the secondary side main winding and the secondary side auxiliary winding may be configured to be partially or entirely shared with each other (the invention described in claim 2).

[0019] In the case of the invention described in claim 3, the insulating transformer has a primary side auxiliary winding, one end of which is connected to the primary side stable potential line, a wiring pattern connected to the other end of the primary side auxiliary winding has a first main body region and a first capacitance forming region continuous therewith, the secondary side stable potential line has a second main body region and a second capacitance forming region continuous therewith, the first and second capacitance forming regions face each other to form a wiring pattern stray capacitance, the wiring pattern stray capacitance is set to a predetermined capacitance value by adjusting the facing area of ​​the first and second capacitance forming regions, and a current according to the capacitance value flows through the wiring pattern stray capacitance in the actual use state, thereby suppressing the magnitude of the combined current of the first noise current and the second noise current to a reference value or less. In this case, the primary side main winding and the primary side auxiliary winding may be configured to be partially or entirely shared with each other (the invention described in claim 4).

[0020] Furthermore, a coupling capacitor element may be provided between the primary side stable potential line and the secondary side stable potential line, and the coupling capacitor element may be provided to substantially short-circuit the primary side stable potential line and the secondary side stable potential line in a frequency band equal to or higher than the switching frequency (invention according to claim 5). Also, a Q-dump resistor element may be inserted in series in at least one of the boundary between the first body region and the first capacitance forming region and the boundary between the second body region and the second capacitance forming region, and the sharpness of the resonance that appears in a frequency band higher than the switching frequency of a resonance system formed by the inter-winding stray capacitance, the wiring pattern stray capacitance, and a parasitic inductance component existing in the vicinity of these may be suppressed by the Q-dump resistor element (invention according to claim 6). Effect of the Invention

[0021] In the switching power supply of the present invention, wiring patterns on different wiring layers of a printed wiring board are opposed to each other to form a wiring pattern capacitance, and the magnitude and direction of the current flowing through the wiring pattern stray capacitance can be freely set by adjusting the opposing area of ​​the wiring patterns and the number of turns and polarity of the auxiliary winding. Therefore, the noise current flowing through the ground resistor in actual use can be effectively suppressed, and a switching power supply with electric shock protection class 2 and small input feedback noise can be easily obtained.

[0022] In addition, in the switching regulator of Patent Document 1, a capacitor element is connected between the noise compensation winding and the input power supply line, but since this capacitor element spans between the primary and secondary, a large, high-voltage product must be selected. However, in the case of the switching power supply device of the present invention, the capacitor spanning between the primary and secondary is a stray capacitance formed by the wiring pattern of the printed wiring board (wiring pattern stray capacitance), so it can be configured very compactly.

[0023] In addition, the present invention is a highly versatile technology, and is not limited to a particular type of inverter circuit to which it can be applied, and can be applied to various insulated inverter circuits, such as a flyback type, a single-ended forward type, a half-bridge type, and a full-bridge type. [Brief description of the drawings]

[0024] [Figure 1] 1 is a circuit diagram showing a first embodiment (flyback type / step-down type) of a switching power supply device of the present invention. [Diagram 2] 1 is a vertical cross-sectional view showing a schematic structure of an insulating transformer, a wiring pattern stray capacitance, and their surroundings in a switching power supply device (flyback type / step-down type) according to a first embodiment. FIG. [Diagram 3] 1A is a common mode equivalent circuit showing an example of the operation of the switching power supply device [flyback type / step-down type] of the first embodiment, and FIG. 1B is a common mode equivalent circuit showing the operation of a comparative example having no wiring pattern stray capacitance and no secondary auxiliary winding. [Figure 4] 1A shows actual measurement data of noise field strength of the switching power supply device [flyback type / step-down type] of the first embodiment, and FIG. 1B shows actual measurement data of a comparative example in which the Q dump resistor is short-circuited. [Diagram 5] FIG. 1A is actual measurement data of the resonance characteristics of a resonance system formed by an isolation transformer, a wiring pattern stray capacitance, and their surrounding parts in a switching power supply device [flyback type / step-down type] of the first embodiment, and FIG. 1B is a circuit diagram showing a method for measuring the resonance characteristics. [Figure 6] 1A is a common mode equivalent circuit showing an example of the operation of a modified example [flyback type / boost type] of the switching power supply device of the first embodiment, and FIG. 1B is a common mode equivalent circuit showing the operation of a comparative example having no wiring pattern stray capacitance and no secondary auxiliary winding. [Figure 7] FIG. 2 is a circuit diagram showing a second embodiment (flyback type / step-down type) of a switching power supply device of the present invention. [Figure 8] FIG. 11 is a longitudinal sectional view showing a schematic structure of an insulating transformer, wiring pattern stray capacitance, and surrounding portions of a switching power supply device (flyback type / step-down type) according to a second embodiment. [Figure 9] 1A is a common mode equivalent circuit showing an example of the operation of a switching power supply device [flyback type / step-down type] of a second embodiment, and FIG. 1B is a common mode equivalent circuit showing the operation of a comparative example having no wiring pattern stray capacitance and no primary side auxiliary winding. [Figure 10] 1A is a common mode equivalent circuit showing the operation of a modified example (flyback type / boost type) of the switching power supply device of the second embodiment, and FIG. 1B is a common mode equivalent circuit of a comparative example having no wiring pattern stray capacitance and no primary side auxiliary winding. [Figure 11] FIG. 11 is a circuit diagram showing a third embodiment (single-ended forward type / step-down type) of a switching power supply device of the present invention. [Figure 12]13A is a common-mode equivalent circuit showing an example of the operation of a switching power supply device [single-ended forward type / step-down type] of the third embodiment, and FIG. 13B is a common-mode equivalent circuit showing the operation of a comparative example having no wiring pattern stray capacitance and no secondary auxiliary winding. [Figure 13] FIG. 11 is a circuit diagram showing a fourth embodiment (single-ended forward type / step-down type) of a switching power supply device of the present invention. [Figure 14] FIG. 1 is a circuit diagram showing another modified example of the switching power supply device of the first embodiment (with a modified structure of the secondary auxiliary winding). [Figure 15] FIG. 11 is a circuit diagram showing another modified example (adding a coupling capacitor element) of the switching power supply device of the first embodiment. [Figure 16] FIG. 1 is a circuit diagram showing a conventional switching power supply device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] <<<Switching power supply device of the first embodiment and its modified examples>>> A first embodiment of the switching power supply device of the present invention and its modified examples will be described below. Here, the same components as those in the conventional switching power supply device 10 are given the same reference numerals and the description thereof will be omitted. <<Switching power supply 38>> First, a switching power supply device 38 which is a first embodiment of the switching power supply device of the present invention will be described with reference to FIGS. 1 to 5. FIG. <Configuration of Switching Power Supply Device 38> The switching power supply 38 is a flyback converter similar to the conventional switching power supply 10, and is a step-down converter in which the output voltage Vo is lower than the input voltage Vi, and is therefore characterized in that the primary main winding 24(1) has a greater number of turns than the secondary main winding 24(2). The switching power supply 38 is obtained by adding a number of components (essential parts of the invention) to the switching power supply 10, and so the following description will focus on the components added to the switching power supply 10.

[0026] 1, in the switching power supply device 38, a secondary auxiliary winding 40(2) which is a third winding is added to the isolation transformer 22, and one end of the secondary auxiliary winding 40(2) is connected to the secondary stable potential line 14(14b). The wiring pattern 42 connected to the other end of the secondary auxiliary winding 40(2) is composed of a second main body region 42h and a second capacitance forming region 42c continuous therewith, and a Q dump resistor element Rh is inserted in series at the boundary between the two regions 42h and 42c.

[0027] The primary side stable potential line 12 (12b) has a first main body region 44h and a first capacitance formation region 44c continuous therewith, and the first capacitance formation region 44c and the second capacitance formation region 42c face each other, forming a wiring pattern stray capacitance Ch.

[0028] The structure of the isolation transformer 22 and its surrounding parts will be briefly explained with reference to Fig. 2. The switching power supply 38 is assembled by mounting circuit components on a printed wiring board 46 having multiple wiring layers inside a base material 46a, and the isolation transformer 22 has three windings 24(1), 24(2), and 40(2) formed by the wiring patterns of the respective wiring layers, and a magnetic core 48 attached to surround them.

[0029] The wiring pattern 42 connected to one end of the secondary auxiliary winding 40(2) has a second main body region 42h located close to the magnetic core 48 and a second capacitance forming region 42c located away from the magnetic core 48, with a Q dump resistor element Rh inserted in series at the boundary between them. The second capacitance forming region 42c faces a first capacitance forming region 44c disposed in another wiring layer, and a wiring pattern stray capacitance Ch is formed therebetween.

[0030] The wiring pattern stray capacitance Ch is set to a predetermined capacitance value by adjusting the opposing areas of the two capacitance generating regions 42c, 44c. The capacitance value to be set will be described in detail later. It is preferable that the capacitance generating regions 42c, 44c are provided at positions where leakage magnetic flux from the magnetic core 48 is unlikely to interlink. If leakage magnetic flux does interlink, eddy currents will flow in the capacitance generating regions 42c, 44c, causing unnecessary loss.

[0031] The stray capacitance to be considered in the actual use state of the switching power supply device 38 is as shown in the circuit diagram of Fig. 1. What differs from the switching power supply device 10 shown in Fig. 16 is that a non-stable potential stray capacitance Cf3 is added that connects the wiring pattern 42 (42h, 42c) at the other end of the secondary-side auxiliary winding 40(2) to the ground line 32, and that a wiring pattern stray capacitance Ch is added between the first capacitance formation region 44c and the second capacitance formation region 42c.

[0032] <Operation of the switching power supply device 38> Next, the operation of the switching power supply device 38 will be described using the common mode equivalent circuit shown in Fig. 3(a). This common mode equivalent circuit is a simplified equivalent circuit that shows the operation in a frequency band of about Fsw to 10 x Fsw. The Q dump resistor element Rh is excluded (short-circuited) from the common mode equivalent circuit because it hardly contributes to the operation in this frequency band. Here, the combined current flowing into the ground line 32 through the unstable potential floating capacitances Cf1, Cf2, ... is defined as a first noise current Icom(1), and the current flowing into the ground line 32 through the secondary side floating capacitance Cy2 is defined as a second noise current Icom(2). In other words, the noise current Icom returning to the switching power supply device 38 through the ground resistance Rs and the primary side floating capacitance Cy1, which is the main cause of input feedback noise, is Icom = Icom(1) + Icom(2).

[0033] Before describing the operation of the switching power supply device 38, the operation of a comparative example 50a that does not have the wiring pattern stray capacitance Ch and the secondary auxiliary winding 40(2) will be described with reference to FIG. 3(b). In the common mode equivalent circuit of FIG. 3(b), the voltage source marked with "Vp" is a voltage source that outputs the voltage Vp generated across the primary main winding 24(1) by the switching of the switching element 26, and the sinusoidal voltages of various frequencies contained in the pulsed voltage Vp become noise sources. The voltage source marked with "Ks·Vp" is a voltage source that outputs the voltage Ks·Vp generated in the secondary main winding 24(2), and Ks is a value (turns ratio) obtained by dividing the number of turns of the secondary main winding 24(2) by the number of turns of the primary main winding 24(1). The switching power supply 38 (and the comparative example 50a) are step-down flyback converters, so the turns ratio Ks is smaller than 1. Additionally, the "+" and "-" signs attached to each voltage source indicate polarity, and the dots attached to the two windings 24(1) and 24(2) in the circuit diagram in FIG. 1 correspond to "+".

[0034] The solid arrows in Fig. 3(b) indicate the direction of the noise current flowing in each part. The current values ​​are numerical examples for ease of explanation, and indicate the noise current values ​​flowing in each part when the noise current flowing in the unstable potential floating capacitance Cf1 is assumed to be 100 μA. In the comparative example 50a, the first noise current Icom(1) is 110 μA, the second noise current Icom(2) is 20 μA, and the noise current Icom that is the main cause of the input feedback noise is 130 μA.

[0035] In contrast, in the switching power supply device 38, in order to suppress the noise current Icom=130 μA of the comparative example 50a, a wiring pattern stray capacitance Ch and a secondary auxiliary winding 40(2) are added. Therefore, the common mode equivalent circuit is supplemented with the wiring pattern stray capacitance Ch, the unstable potential stray capacitance Cf3, and the voltage source labeled "Kh2·Vp" as shown in FIG. 3(a).

[0036] The voltage source labeled "Kh2·Vp" is a voltage source that outputs a voltage Kh2·Vp generated in the secondary auxiliary winding 40(2), where Kh2 is the value (turns ratio) obtained by dividing the number of turns of the secondary auxiliary winding 40(2) by the number of turns of the primary main winding 24(1). The signs "+" and "-" labeled to this voltage source indicate polarity, and the dot labeled to the secondary auxiliary winding 40(2) in the circuit diagram of FIG. 1 corresponds to "+".

[0037] In the switching power supply device 38, in addition to the current indicated by the solid arrow in Fig. 3(b), a current indicated by the dashed arrow is generated. As a result, the first noise current Icom(1) is 120 μA, the second noise current Icom(2) is -120 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0038] As can be seen from FIG. 3(a), the current flowing through the voltage source labeled "Kh2·Vp" and the wiring pattern stray capacitance Ch among the currents indicated by the dashed arrows is the cancellation current for suppressing the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the wiring pattern stray capacitance Ch and the number of turns of the secondary auxiliary winding 40(2). By setting the noise current Icom to be equal to or less than the reference value, the input feedback noise can be suppressed. For example, the standard value for the noise terminal voltage (150k to 30MHz), which is one of the evaluation items of the EMI standard, can be easily cleared.

[0039] In the switching power supply 38, one end of the secondary auxiliary winding 40(2) is connected to the secondary ground line 14b, but the same effect can be obtained by connecting it to the secondary power supply line 14a. Also, in the switching power supply 38, the first body region 44h and the first capacitance forming region 44c are provided on the primary ground line 12b, but the same effect can be obtained by providing them on the primary power supply line 12a.

[0040] Next, the function of the Q dump resistor element Rh will be described with reference to Figures 4 and 5. The Q dump resistor element Rh is effective in suppressing noise electric field strength (30 MHz to 1 GHz), which is one of the evaluation items for radiated interference waves.

[0041] Fig. 4(a) shows actual measurement data of the noise field strength of the switching power supply device 38, and Fig. 4(b) shows actual measurement data of the comparative example 50b in which the Q dump resistor element Rh is shorted. Comparing the two sets of actual measurement data, the level of 35M to 65MHz is relatively high when there is no Q dump resistor element Rh, whereas the level of 35M to 65MHz drops by several dB when the Q dump resistor element RH is provided. The reason for this can be explained based on the data in Fig. 5.

[0042] Figure 5(a) shows the measured data of the frequency characteristics of the combined interwinding stray capacitance Ct and wiring pattern stray capacitance Ch (composite stray capacitance). The combined stray capacitance was calculated by assembling the measurement circuit shown in Figure 5(b) and measuring the voltage V applied by the oscillator OSC and the current I flowing to calculate Z=V / I, which was then converted into a capacitance value by treating it as the impedance of a pure capacitor.

[0043] Without the Q dump resistor Rh, a resonance point occurred at about 60MHz, and the composite stray capacitance increased significantly from 20M to 70MHz. When the Q dump resistor Rh (47Ω) was provided, the resonance point remained at about 60MHz, but the increase in the composite stray capacitance from 20M to 70MHz was suppressed to a small level. This is because the provision of the Q dump resistor Rh (47Ω in this example) significantly suppressed the sharpness of the resonance that appears in the frequency band (about 60MHz in this example) that is sufficiently higher than the switching frequency Fsw in the resonant system formed by the interwinding stray capacitance Ct, the wiring pattern stray capacitance Ch, and the parasitic inductance components present in the vicinity of these.

[0044] Generally, this type of resonance phenomenon is known to be likely to cause an increase in the radiated interference waves from the switching power supply device. However, even if an unintentional resonance system is formed in the isolation transformer 22 and its peripheral part like the switching power supply device 38, by connecting the Q-damping resistor element Rh in series near the wiring pattern stray capacitance Ch, unnecessary radiated interference waves can be effectively suppressed.

[0045] Note that in the switching power supply device 38, the Q-damping resistor element Rh is provided at the boundary between the second main body region 42h and the second capacitance forming region 42c, but it may also be provided at the boundary between the first main body region 44h and the first capacitance forming region 44c, and substantially the same effect can be obtained.

[0046] <<Modified Switching Power Supply Device 38x>> Next, a modified example of the switching power supply device 38, the switching power supply device 38x, will be described with reference to FIG. 6. <Configuration of Switching Power Supply Device 38x> Since the above-mentioned switching power supply device 38 is a step-down converter [Vi>Vo], the value (turns ratio Ks) obtained by dividing the number of turns of the secondary-side main winding 24(2) by the number of turns of the primary-side main winding 24(1) is less than 1. Also, since it is a step-down converter, one end of the secondary-side auxiliary winding 40(2) without a dot is connected to the secondary-side stable potential line 14.

[0047] In contrast, the modified example of the switching power supply device 38x is a step-up converter [Vi<Vo], so the turns ratio Ks between the primary-side main winding 24(1) and the secondary-side main winding 24(2) is greater than 1, and there is a difference in that one end of the secondary-side auxiliary winding 40(2) with a dot is connected to the secondary-side stable potential line 14. The other configurations are the same.

[0048] <Operation of Switching Power Supply Device 38x> Next, the operation of the switching power supply device 38x will be described using the common mode equivalent circuit shown in Fig. 6(a). This common mode equivalent circuit is also a simplified equivalent circuit that shows the operation in a frequency band of about Fsw to 10 × Fsw, where Fsw is the switching frequency. Before describing the operation of the switching power supply device 38x, the operation of a comparative example 50b without the wiring pattern stray capacitance Ch and the secondary auxiliary winding 40(2) will be described with reference to FIG. 6(b). The current values ​​shown in FIG. 6(b) are numerical examples for ease of explanation, and show the noise current values ​​flowing through each part when the noise current flowing through the unstable potential stray capacitance Cf1 is assumed to be 10 μA. In the comparative example 50b, the first noise current Icom(1) is 110 μA, the second noise current Icom(2) is -130 μA, and the noise current Icom, which is the main cause of the input feedback noise, is -20 μA. Since the comparative example 50b has Ks>1, there are differences, such as the direction of the current flowing through the interwinding stray capacitance Ct being opposite to that in the case of Ks<1 (FIG. 3(b)).

[0049] In contrast, in the switching power supply device 38x, in order to suppress the noise current Icom=-20μA of the comparative example 50b, a wiring pattern stray capacitance Ch and a secondary side auxiliary winding 40(2) are added. Therefore, the common mode equivalent circuit is supplemented with the wiring pattern stray capacitance Ch, the unstable potential stray capacitance Cf3, and the voltage source labeled "Kh2·Vp" as shown in FIG. 6(a).

[0050] The voltage source labeled "Kh2·Vp" is a voltage source that outputs the voltage Kh2·Vp generated in the secondary auxiliary winding 40(2). However, since the polarity of the secondary auxiliary winding 40(2) is reversed in the switching power supply 38x, the positions of "+" and "-" are reversed compared to the switching power supply 30 (FIG. 3(a)).

[0051] In the switching power supply device 38x, in addition to the current indicated by the solid arrow in Fig. 6(b), a current indicated by the dashed arrow is generated. As a result, the first noise current Icom(1) is 100 μA, the second noise current Icom(2) is -100 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0052] As can be seen from Figure 6(a), among the currents indicated by the dashed arrows, the current flowing through the voltage source labeled "Kh2·Vp" and the wiring pattern stray capacitance Ch is a cancellation current that suppresses the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the wiring pattern stray capacitance Ch and the number of turns of the secondary auxiliary winding 40(2), and by setting the noise current Icom to be equal to or less than a reference value, the input feedback noise can be suppressed.

[0053] In this way, the step-up switching power supply device 38x also operates in a manner similar to that of the step-down switching power supply device 38, and provides similar effects. <<Summary of switching power supply unit 38, 38x>> In the switching power supply devices 38, 38x, wiring patterns on different wiring layers of the printed wiring board 46 are opposed to each other to form a wiring pattern stray capacitance Ch, and the magnitude and direction of the current flowing through the wiring pattern stray capacitance Ch can be freely set by the opposing area of ​​the wiring patterns and the number of turns and polarity of the secondary auxiliary winding 40(2). Therefore, the noise current Icom flowing through the ground resistance Rs in actual use can be effectively suppressed, and a switching power supply device with electric shock protection class 2 and small input feedback noise can be obtained.

[0054] In addition, in the switching regulator of Patent Document 1, a capacitor element is connected between the noise compensation winding and the input power supply line, but since this capacitor element spans between the primary and secondary, a large, high-voltage product must be selected. However, in the case of switching power supply devices 38, 38x, the capacitor spanning between the primary and secondary is a stray capacitance (wiring pattern stray capacitance Ch) formed by the wiring pattern of the printed wiring board, so it can be configured very compactly.

[0055] <<<Switching power supply device of the second embodiment and its modified example>>> Next, a second embodiment of the switching power supply device of the present invention and its modified example will be described. Here, the same components as those in the conventional switching power supply device 10 are given the same reference numerals and the description thereof will be omitted. <<Switching power supply unit 52>> First, a switching power supply device 52 according to the second embodiment will be described with reference to FIGS. <Configuration of Switching Power Supply Device 52> The switching power supply 52 is a flyback converter like the conventional switching power supply 10, and is also a step-down converter in which the output voltage Vo is lower than the input voltage Vi, and is therefore characterized in that the primary main winding 24(1) has a greater number of turns than the secondary main winding 24(2). The switching power supply 52 is obtained by adding a number of components (essential parts of the invention) to the switching power supply 10, and the following description will focus on the components added to the switching power supply 10.

[0056] 7, in the switching power supply device 52, a primary side auxiliary winding 40(1) which is a third winding is added to the isolation transformer 22, and one end of the primary side auxiliary winding 40(1) is connected to the primary side stable potential line 12(12a). The wiring pattern 54 connected to the other end of the primary side auxiliary winding 40(1) is composed of a first main body region 54h and a first capacitance forming region 54c continuous therewith, and a Q dump resistor element Rh is inserted in series at the boundary between the two regions 54h and 54c.

[0057] The secondary side stable potential line 14 (14b) has a second main body region 56h and a second capacitance formation region 56c continuous therewith, and the first capacitance formation region 54c and the second capacitance formation region 56c face each other, forming a wiring pattern stray capacitance Ch.

[0058] The structure of the isolation transformer 22 and its surrounding parts will be briefly explained with reference to Fig. 8. The switching power supply 52 is assembled by mounting circuit components on a printed wiring board 46 having multiple wiring layers inside a base material 46a, and the isolation transformer 22 has three windings 24(1), 24(2), and 40(1) formed by the wiring patterns of the respective wiring layers, and is structured so that a magnetic core 48 is attached to surround these.

[0059] The wiring pattern 54 connected to one end of the primary-side auxiliary winding 40(1) has a first main body region 54h located close to the magnetic core 48 and a first capacitance-forming region 54c located away from the magnetic core 48, with a Q-dump resistor element Rh inserted in series at the boundary between them. The first capacitance-forming region 54c faces a second capacitance-forming region 56c disposed in another wiring layer, and a wiring pattern stray capacitance Ch is formed therebetween.

[0060] The wiring pattern stray capacitance Ch is set to a predetermined capacitance value by adjusting the opposing areas of the two capacitance forming regions 54c, 56c. The capacitance value to be set will be described in detail later. It is preferable that the capacitance forming regions 54c, 56c are provided at positions where leakage magnetic flux from the magnetic core 48 is unlikely to interlink. If leakage magnetic flux does interlink, eddy currents will flow in the capacitance forming regions 54c, 56c, causing unnecessary loss.

[0061] The stray capacitance to be considered in the actual use state of the switching power supply device 52 is as shown in the circuit diagram of Fig. 7. What differs from the switching power supply device 10 shown in Fig. 16 is that a non-stable potential stray capacitance Cf4 is added that connects the wiring pattern 54 (54h, 54c) at the other end of the primary side auxiliary winding 40(1) to the ground line 32, and that a wiring pattern stray capacitance Ch is added between the first capacitance formation region 54c and the second capacitance formation region 56c.

[0062] <Operation of the switching power supply device 52> Next, the operation of the switching power supply device 52 will be described using the common mode equivalent circuit shown in Fig. 9(a). This common mode equivalent circuit is also a simplified equivalent circuit that shows the operation in a frequency band of about Fsw to 10 x Fsw. The Q dump resistor element Rh has been excluded (short-circuited) from the common mode equivalent circuit because it hardly contributes to the operation in this frequency band. Also, the meanings of the first noise current Icom(1), the second noise current Icom(2), and the noise current Icom that appear in this description are the same as those described above.

[0063] Before describing the operation of the switching power supply device 52, the operation of a comparative example 50c that does not have the wiring pattern stray capacitance Ch and the primary side auxiliary winding 40(1) will be described with reference to FIG. 9(b). The common mode equivalent circuit of the comparative example 50c has the same configuration as the common mode equivalent circuit of the comparative example 50a described above (FIG. 3(b)). The current values ​​are also numerical examples for ease of explanation, and show the values ​​of the noise current flowing in each part when the noise current flowing in the unstable potential stray capacitance Cf1 is assumed to be 100 μA. In the case of the comparative example 50c, the first noise current Icom(1) is 110 μA, the second noise current Icom(2) is 20 μA, and the noise current Icom that is the main cause of the input feedback noise is 130 μA.

[0064] In contrast, in the switching power supply device 52, in order to suppress the noise current Icom=130 μA of the comparative example 50c, a wiring pattern stray capacitance Ch and a secondary auxiliary winding 40(2) are added. Therefore, the common mode equivalent circuit is supplemented with the wiring pattern stray capacitance Ch, the unstable potential stray capacitance Cf4, and a voltage source labeled "Kh1·Vp" as shown in FIG. 9(a).

[0065] The voltage source labeled "Kh1·Vp" is a voltage source that outputs a voltage Kh1·Vp generated in the primary-side auxiliary winding 40(1), where Kh1 is the value (turns ratio) obtained by dividing the number of turns of the primary-side auxiliary winding 40(1) by the number of turns of the primary-side main winding 24(1). The signs "+" and "-" labeled to this voltage source indicate polarity, and the dot labeled to the primary-side auxiliary winding 40(1) in the circuit diagram of FIG. 7 corresponds to "+".

[0066] In the switching power supply device 52, in addition to the current indicated by the solid arrow in Fig. 9(b), a current indicated by the dashed arrow is generated. As a result, the first noise current Icom(1) is 100 μA, the second noise current Icom(2) is -100 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0067] As can be seen from FIG. 9(a), the current flowing through the voltage source labeled "Kh1·Vp" and the wiring pattern stray capacitance Ch among the currents indicated by the dashed arrows is the cancellation current for suppressing the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the wiring pattern stray capacitance Ch and the number of turns of the primary side auxiliary winding 40(1). By setting the noise current Icom to be equal to or less than the reference value, the input feedback noise can be suppressed. For example, the standard value for the noise terminal voltage (150k to 30MHz), which is one of the evaluation items of the EMI standard, can be easily cleared.

[0068] In the switching power supply device 52, one end of the primary side auxiliary winding 40(1) is connected to the primary side power supply line 12a, but the same effect can be obtained by connecting it to the primary side ground line 12b. Also, in the switching power supply device 52, the second main body region 56h and the second capacitance forming region 56c are provided on the secondary side ground line 14b, but the same effect can be obtained by providing them on the secondary side power supply line 14a.

[0069] The function of the Q-dump resistor element Rh is the same as that of the Q-dump resistor element Rh of the switching power supply device 38 described above. It suppresses the sharpness of resonance that appears in a frequency band sufficiently higher than the switching frequency Fsw of a resonance system formed by the inter-winding stray capacitance Ct, the wiring pattern stray capacitance Ch, and the parasitic inductance components existing in the vicinity thereof, thereby effectively suppressing unnecessary radiation interference waves.

[0070] Note that in the switching power supply device 52, the Q-dump resistor element Rh is provided at the boundary between the first main body region 54h and the first capacitance forming region 54c, but it may also be provided at the boundary between the second main body region 56h and the second capacitance forming region 56c, and substantially the same effect can be obtained.

[0071] <<Switching Power Supply Device 52x of the Modified Example>> Next, a switching power supply device 52x, which is a modified example of the switching power supply device 52, will be described with reference to FIG. 10. <Configuration of the Switching Power Supply Device 52x> Since the above-described switching power supply device 52 is a step-down converter [Vi>Vo], the value (turns ratio Ks) obtained by dividing the number of turns of the secondary-side main winding 24(2) by the number of turns of the primary-side main winding 24(1) is less than 1. Also, since it is a step-down converter, one end of the primary-side auxiliary winding 40(1) with a dot is connected to the primary-side stable potential line 12.

[0072] In contrast, the switching power supply device 52x of the modified example is a step-up converter [Vi<Vo], and the turns ratio Ks between the primary-side main winding 24(1) and the secondary-side main winding 24(2) is greater than 1, and one end of the primary-side auxiliary winding 40(1) without a dot is connected to the primary-side stable potential line 12. The other configurations are the same. <Operation of the Switching Power Supply Device 52x> Next, the operation of the switching power supply device 52x will be described using the common-mode equivalent circuit shown in FIG. 6(a). This common-mode equivalent circuit is also a simplified equivalent circuit that shows the operation in a frequency band of about Fsw to 10×Fsw with respect to the switching frequency Fsw.

[0073] Before describing the operation of the switching power supply device 52x, the operation of a comparative example 50d that does not have the wiring pattern stray capacitance Ch and the primary side auxiliary winding 40(1) will be described with reference to FIG. 10(b). The common mode equivalent circuit of the comparative example 50d is the same as the common mode equivalent circuit of the comparative example 50b described above (FIG. 6(b)), and the current values ​​are also numerical examples for ease of explanation, showing the values ​​of the noise current flowing in each part when the noise current flowing in the unstable potential stray capacitance Cf1 is assumed to be 10 μA. Therefore, in the comparative example 50d, the first noise current Icom(1) is 110 μA, the second noise current Icom(2) is -130 μA, and the noise current Icom that is the main cause of the input feedback noise is -20 μA. Since the comparative example 50d has Ks>1, there are differences, such as the direction of the current flowing in the inter-winding stray capacitance Ct being opposite to that in the case of Ks<1 (FIG. 9(b)).

[0074] In contrast, in the switching power supply device 52x, in order to suppress the noise current Icom=-20μA of the comparative example 50d, a wiring pattern stray capacitance Ch and a primary side auxiliary winding 40(1) are added. Therefore, the common mode equivalent circuit is supplemented with the wiring pattern stray capacitance Ch, the unstable potential stray capacitance Cf3, and a voltage source labeled "Kh1·Vp" as shown in FIG.

[0075] The voltage source labeled "Kh1·Vp" is a voltage source that outputs the voltage Kh1·Vp generated in the primary-side auxiliary winding 40(1). However, since the polarity of the primary-side auxiliary winding 40(1) is reversed in the switching power supply 52x, the positions of the "+" and "-" labeled this voltage source are reversed when compared with the switching power supply 52 (FIG. 9(a)).

[0076] In the switching power supply device 52x, in addition to the current indicated by the solid arrow in Fig. 10(b), a current indicated by the dashed arrow is generated. As a result, the first noise current Icom(1) is 120 μA, the second noise current Icom(2) is -120 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0077] As can be seen from Figure 10(a), among the currents indicated by the dashed arrows, the current flowing through the voltage source labeled "Kh1·Vp" and the wiring pattern stray capacitance Ch is a cancellation current that suppresses the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the wiring pattern stray capacitance Ch and the number of turns of the primary side auxiliary winding 40(1), and by setting the noise current Icom to be equal to or less than a reference value, the input feedback noise can be suppressed.

[0078] In this way, the step-up switching power supply device 52x operates in a similar manner to the step-down switching power supply device 52, and provides similar effects.

[0079] <<Summary of Switching Power Supply Unit 52, 52x>> In the switching power supply devices 52 and 52x, wiring patterns on different wiring layers of the printed wiring board 46 are opposed to each other to form a wiring pattern stray capacitance Ch, and the magnitude and direction of the current flowing through the wiring pattern stray capacitance Ch can be freely set by the opposing area of ​​the wiring patterns and the number of turns and polarity of the primary-side auxiliary winding 40(1). Therefore, the noise current Icom flowing through the ground resistance Rs in actual use can be effectively suppressed, and a switching power supply device with electric shock protection class 2 and small input feedback noise can be obtained. Also, similar to the above-described switching power supply devices 38 and 38x, the switching regulator of Patent Document 1 can be configured more compactly.

[0080] <<<Switching power supply device of the third embodiment and its modified example>>> Next, a third embodiment of the switching power supply device of the present invention and its modified example will be described. Here, the same components as those in the conventional switching power supply device 10 are given the same reference numerals and the description thereof will be omitted. <<Switching power supply unit 58>> First, a switching power supply device 58 of the third embodiment will be described with reference to Figures 11 and 12. Here, the same components as those of the conventional switching power supply device 10 are given the same reference numerals and the description thereof will be omitted. <Configuration of Switching Power Supply Device 58> While the conventional switching power supply 10 is a flyback converter, the switching power supply 58 is a single-ended forward converter, in which the rectifier circuit 28 is two diodes 28b, 28c, the smoothing circuit 30 is an inductor 30a and an output interphase capacitor element 18, and several other components that are essential to the present invention are added. In addition, the switching power supply 58 is a step-down converter in which the output voltage Vo is lower than the input voltage Vi, and is therefore characterized in that the primary main winding 24(1) has more turns than the secondary main winding 24(2). The following describes the configuration of the switching power supply 58, focusing on the added components (essential parts of the invention).

[0081] 11, in a switching power supply device 58, a secondary auxiliary winding 40(2) which is a third winding is added to the isolation transformer 22, and one end of the secondary auxiliary winding 40(2) is connected to the secondary stable potential line 14(14b). The wiring pattern 42 connected to the other end of the secondary auxiliary winding 40(2) is composed of a second main body region 42h and a second capacitance forming region 42c continuous therewith, and a Q dump resistor Rh is inserted in series at the boundary between the two regions 42h and 42c.

[0082] The primary side stable potential line 12 (12b) has a first main body region 44h and a first capacitance formation region 44c continuous therewith, and the first capacitance formation region 44c and the second capacitance formation region 42c face each other, forming a wiring pattern stray capacitance Ch.

[0083] As shown in the circuit diagram of FIG. 11, the stray capacitances to be considered when the switching power supply device 58 is actually used are the primary-side stray capacitance Cy1 connecting the primary-side stable potential line 12 and the ground line 32, the secondary-side stray capacitance Cy2 connecting the secondary-side stable potential line 14 and the ground line 32, the inter-winding stray capacitance Ct formed between the primary-side main winding 24(1) and the secondary-side main winding 24(2), and the wiring pattern stray capacitance Ch formed between the first capacitance formation region 44c and the second capacitance formation region 42c.

[0084] Further, examples of unstable potential floating capacitances to be taken into consideration include an unstable potential floating capacitance Cf1 connecting the connection point of the primary main winding 24(1) and the switching element 26 with the ground line 32, an unstable potential floating capacitance Cf2 connecting the connection point of the secondary main winding 24(2) and the rectifier circuit 28(28a) with the ground line 32, an unstable potential floating capacitance Cf3 connecting the wiring pattern 42(42h, 42c) with the ground line 32, and an unstable potential floating capacitance Cf5 connecting the diode 28a, the inductor 30, the connection point 60, and the ground line 32.

[0085] <Operation of the switching power supply device 58> Next, the operation of the switching power supply device 58 will be described using the common mode equivalent circuit shown in Fig. 12(a). This common mode equivalent circuit is also a simplified equivalent circuit that shows the operation in a frequency band of about Fsw to 10 x Fsw. The Q dump resistor element Rh has been excluded (short-circuited) from the common mode equivalent circuit because it hardly contributes to the operation in this frequency band. The meanings of the first noise current Icom(1), the second noise current Icom(2), and the noise current Icom that appear in this description are the same as those described above.

[0086] Before describing the operation of the switching power supply device 58, the operation of a comparative example 50e that does not have the wiring pattern stray capacitance Ch and the secondary auxiliary winding 40(2) will be described with reference to FIG. 12(b). In the common mode equivalent circuit of FIG. 12(b), the voltage source marked with "Vp" is a voltage source that generates a voltage Vp across the primary main winding 24(1) by switching the switching element 26, and sinusoidal voltages of various frequencies contained in the pulsed voltage Vp become noise sources. The voltage source marked with "Ks·Vp" is a voltage source that outputs a voltage Ks·Vp generated in the secondary main winding 24(2), where Ks is a value (turns ratio) obtained by dividing the number of turns of the secondary main winding 24(2) by the number of turns of the primary main winding 24(1). The voltage source marked with "Kc·Vp" is a voltage source that outputs a voltage Kc·Vp generated in the inductor 30a, where Kc is a coefficient indicating the amplitude ratio with respect to the voltage Vp. In addition, the signs "+" and "-" attached to each voltage source indicate polarity, and in the circuit diagram of FIG. 11, the dots attached to the two windings 24(1), 24(2) and the inductor 30 correspond to "+".

[0087] 12(b) are numerical examples for ease of explanation, and show the noise current values ​​flowing in each part when the noise current flowing in the unstable potential floating capacitance Cf1 is assumed to be 100 μA. In the comparative example 50e, the first noise current Icom(1) is 115 μA, the second noise current Icom(2) is 15 μA, and the noise current Icom that is the main cause of the input feedback noise is 130 μA.

[0088] In contrast, in the switching power supply device 58, in order to suppress the noise current Icom=130 μA of the comparative example 50e, a wiring pattern stray capacitance Ch and a secondary auxiliary winding 40(2) are added. Therefore, the common mode equivalent circuit is added with the wiring pattern stray capacitance Ch, the unstable potential stray capacitance Cf3, and the voltage source marked "Kh2·Vp" as shown in FIG.

[0089] The voltage source labeled "Kh2·Vp" is a voltage source that outputs a voltage Kh2·Vp generated in the secondary auxiliary winding 40(2), and Kh2 is the value (turns ratio) obtained by dividing the number of turns of the secondary auxiliary winding 40(2) by the number of turns of the primary main winding 24(1). The signs "+" and "-" labeled to this voltage source indicate polarity, and the dot labeled to the secondary auxiliary winding 40(2) in the circuit diagram of FIG. 11 corresponds to "+".

[0090] In the switching power supply device 58, in addition to the current indicated by the solid arrow in Fig. 12(b), a current indicated by the dashed arrow is generated. As a result, the first noise current Icom(1) is 125 μA, the second noise current Icom(2) is -125 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0091] As can be seen from FIG. 12(a), the current flowing through the voltage source labeled "Kh2·Vp" and the wiring pattern stray capacitance Ch among the currents indicated by the dashed arrows is a cancellation current for suppressing the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the wiring pattern stray capacitance Ch and the number of turns of the secondary auxiliary winding 40(2). By setting the noise current Icom to be equal to or less than the reference value, the input feedback noise can be suppressed. For example, the standard value for the noise terminal voltage (150k to 30MHz), which is one of the evaluation items of the EMI standard, can be easily cleared.

[0092] In the switching power supply device 58, one end of the secondary auxiliary winding 40(2) is connected to the secondary ground line 14b, but the same effect can be obtained by connecting it to the secondary power supply line 14a. Also, in the switching power supply device 58, the first body region 44h and the first capacitance forming region 44c are provided on the primary ground line 12b, but the same effect can be obtained by providing them on the primary power supply line 12a.

[0093] The function of the Q-dump resistor element Rh is the same as that of the Q-dump resistor element Rh of the switching power supply device 38 described above. It suppresses the sharpness of resonance that appears in a frequency band sufficiently higher than the switching frequency Fsw of a resonance system formed by the inter-turn parasitic capacitance Ct, the wiring pattern parasitic capacitance Ch, and the parasitic inductance components existing in the vicinity thereof, thereby effectively suppressing unnecessary radiation interference waves.

[0094] In the switching power supply device 58, the Q-dump resistor element Rh is provided at the boundary between the second main body region 42h and the second capacitance forming region 42c, but it may be provided at the boundary between the first main body region 44h and the first capacitance forming region 44c, and substantially the same effect can be obtained.

[0095] <<Modified Switching Power Supply Device 58x>> Next, a switching power supply device 58x, which is a modified example of the switching power supply device 58, will be described.

[0096] Since the above-described switching power supply device 58 is a step-down converter [Vi>Vo], the value (turns ratio Ks) obtained by dividing the number of turns of the secondary-side main winding 24(2) by the number of turns of the primary-side main winding 24(1) is less than 1. Also, since it is a step-down converter, one end of the secondary-side auxiliary winding 40(2) without a dot is connected to the secondary-side stable potential line 14.

[0097] In contrast, the modified example switching power supply device 58x is a step-up converter [Vi<Vo], and the turns ratio Ks between the primary-side main winding 24(1) and the secondary-side main winding 24(2) is greater than 1. The difference is that one end of the secondary-side auxiliary winding 40(2) with a dot is connected to the secondary-side stable potential line 14. Other configurations are the same.

[0098] The operation description of the switching power supply device 58x is omitted. Even in the step-up switching power supply device 58x, operations similar to those of the step-down switching power supply device 58 are performed, and the same effects are obtained.

[0099] <<Summary of Switching Power Supply Unit 58, 58x>> As described above, the switching power supply devices 58, 58x (single-ended forward converters) also perform operations similar to those of the switching power supply devices 38, 38x (flyback converters), and provide similar effects.

[0100] <<<Switching power supply device of the fourth embodiment and its modified example>>> Next, a fourth embodiment of the switching power supply device of the present invention and its modified example will be described. Here, the same components as those in the conventional switching power supply device 10 are given the same reference numerals and the description thereof will be omitted. <<Switching power supply unit 62>> First, a switching power supply device 62 according to the fourth embodiment will be described with reference to FIG. <Configuration of Switching Power Supply Device 62> While the conventional switching power supply 10 is a flyback converter, the switching power supply 62 is a single-ended forward converter, in which the rectifier circuit 28 is two diodes 28b, 28c, the smoothing circuit 30 is an inductor 30a and an output interphase capacitor element 18, and several other components that are essential to the present invention are added. In addition, the switching power supply 62 is a step-down converter in which the output voltage Vo is lower than the input voltage Vi, and is therefore characterized in that the primary main winding 24(1) has a greater number of turns than the secondary main winding 24(2). The following describes the configuration of the switching power supply 62, focusing on the added components (essential parts of the invention).

[0101] 13, in the switching power supply device 62, a primary side auxiliary winding 40(1) which is a third winding is added to the isolation transformer 22, and one end of the primary side auxiliary winding 40(1) is connected to the primary side stable potential line 12(12a). The wiring pattern 54 connected to the other end of the primary side auxiliary winding 40(1) is composed of a first main body region 54h and a first capacitance forming region 54c continuous therewith, and a Q dump resistor element Rh is inserted in series at the boundary between the two regions 54h and 54c.

[0102] The secondary side stable potential line 14 (14a) has a second main body region 56h and a second capacitance formation region 56c continuous therewith, and the first capacitance formation region 54c and the second capacitance formation region 56c face each other, forming a wiring pattern stray capacitance Ch.

[0103] As shown in the circuit diagram of FIG. 13, the stray capacitances to be considered when the switching power supply device 62 is actually used are the primary-side stray capacitance Cy1 connecting the primary-side stable potential line 12 and the ground line 32, the secondary-side stray capacitance Cy2 connecting the secondary-side stable potential line 14 and the ground line 32, the inter-winding stray capacitance Ct formed between the primary-side main winding 24(1) and the secondary-side main winding 24(2), and the wiring pattern stray capacitance Ch formed between the first capacitance formation region 54c and the second capacitance formation region 56c.

[0104] Further, examples of unstable potential floating capacitances that should be taken into consideration include an unstable potential floating capacitance Cf1 that connects the connection point of the primary main winding 24(1) and the switching element 26 with the ground line 32, an unstable potential floating capacitance Cf2 that connects the connection point of the secondary main winding 24(2) and the rectifier circuit 28 (28a) with the ground line 32, an unstable potential floating capacitance Cf4 that connects the wiring pattern 54 (54h, 54c) and the ground line 32, and an unstable potential floating capacitance Cf5 that connects the diode 28a and the inductor 30 with the connection point 60 and the ground line 32.

[0105] <Operation of the switching power supply device 62> A description of the operation of the switching power supply device 62 will be omitted. The switching power supply device 62 (single-ended forward converter) also performs operations similar to those of the switching power supply device 52 (flyback converter) and the switching power supply device 58 (single-ended forward converter), and provides similar effects.

[0106] <<Modification of Switching Power Supply Device 62x>> Next, a switching power supply device 62x, which is a modification of the switching power supply device 62, will be described. Since the above switching power supply device 62 is a step-down converter [Vi>Vo], the value obtained by dividing the number of turns of the secondary-side main winding 24(2) by the number of turns of the primary-side main winding 24(1) (turns ratio Ks) is less than 1. Also, since it is a step-down converter, one end of the primary-side auxiliary winding 40(1) with a dot is connected to the primary-side stable potential line 14.

[0107] On the other hand, the switching power supply device 62x of the modified example is a step-up converter [Vi<Vo], and the turns ratio Ks of the primary-side main winding 24(1) and the secondary-side main winding 24(2) is greater than 1. There is a difference in that one end of the primary-side auxiliary winding 40(1) without a dot is connected to the primary-side stable potential line 12. Other configurations are the same.

[0108] Although the operation description of the switching power supply device 62x is omitted, in the step-up switching power supply device 62x as well, an operation similar to that of the step-down switching power supply device 62 is performed, and similar effects are obtained.

[0109] <<Summary of Switching Power Supply Devices 62 and 62x>> As described above, in the switching power supply devices 62 and 62x (single-ended forward converters) as well, an operation similar to that of the switching power supply devices 52 and 52x (flyback converters) is performed, and similar effects are obtained.

[0110] <<<Other Embodiments and Modified Examples, etc.>>> The switching power supply device of the present invention is not limited to the above-mentioned embodiment and modified examples. For example, in the switching power supply device 38 of FIG. 1, the secondary main winding 24(2) and the secondary auxiliary winding 40(2) can be used in part or in whole. Since the switching power supply device 38 is a step-down type, as in a switching power supply device 38y shown in FIG. 14, a structure is adopted in which an additional winding 66(2) is connected in series to one end of the secondary main winding 24(2), and the secondary main winding 24(2) and the additional winding (2) as a whole can be used as the secondary auxiliary winding 40(2). Even with such a modification, the same operation as the above-mentioned switching power supply device 38 can be performed and the same effect can be obtained. Also, in a switching power supply device 52x in which the switching power supply device 52 of FIG. 7 is a step-up type, the primary main winding 24(1) and the primary auxiliary winding 40(1) can be used in part or in whole. The statement that "if conditions are met, the auxiliary winding and the main winding can be partially or entirely used in common" also applies to converters other than the flyback converter and single-ended forward converter.

[0111] 15, a coupling capacitor element 66 that essentially shorts the primary side stable potential line 12 and the secondary side stable potential line 14 in a frequency band equal to or higher than the switching frequency Fsw may be connected between the primary side stable potential line 12 and the secondary side stable potential line 14. By providing the coupling capacitor element 66, an effect is obtained in that noise current that tends to flow out toward the external load 36 is recovered to the primary side through the coupling capacitor element 66. The phrase "coupling capacitor element may be provided" also applies to converters other than a flyback converter or a single-ended forward converter.

[0112] Additionally, the switching power supply devices of the above embodiments and modifications are all DC-DC converters of electric shock protection class 2, but the present invention is also applicable to AC-DC converters of electric shock protection class 2. An AC-DC converter of electric shock protection class 2 can be configured by providing a rectifying and smoothing circuit (a circuit that rectifies and smoothes the AC voltage e output by the input power supply to generate the input voltage Vi) in the preceding stage of the input interphase capacitor element 16 of the above DC-DC converter, and similar operational effects can be obtained.

[0113] The common mode equivalent circuit used to explain the operation of the above embodiment and modified examples is merely a simplified equivalent circuit, and does not represent the actual operation with high accuracy. Therefore, it is practical to carry out experiments using a prototype and simple calculations using the common mode equivalent circuit in parallel, derive optimal values ​​for the number of turns of the auxiliary winding and the value of the wiring pattern stray capacitance based on the results, and then start pattern design (new design, improved design) of the printed wiring board. [Explanation of symbols]

[0114] 10,38,38x,38y,38z,52,52x,58,62 Switching power supply 12 Primary side stable potential line 12a Primary power line 12b Primary side ground line 14 Secondary side stable potential line 14a Secondary power line 16 Primary side interphase capacitor element 18 Secondary interphase capacitor element 20 Inverter circuit 22 Isolation transformer 24(1) Primary main winding 24(2) Secondary main winding 26 Switching element 28 Rectifier circuit 30 Smoothing circuit 32 Ground Line 34 Input power 36 External Load 40(2) Secondary auxiliary winding 42 Wiring Pattern 42h Second body region 42c Second capacitance forming region 44h First body area (primary stable potential line) 44c First capacitance formation area (primary side stable potential line) 46 Printed Wiring Board 46a Base material 48 Magnetic Core 50a to 50e Comparative Example Switching Power Supply Device 54 Wiring Pattern 54h First body area 54c First capacitance forming region 56h Second body area (secondary stable potential line) 56c Second capacitance formation area (secondary side stable potential line) 60 Connection Points 64(2) Additional winding 66 Coupling capacitor element Cf1~Cf5 Unstable potential floating capacitance Ch Wiring pattern stray capacitance Ct: Interwinding stray capacitance Cy1 Primary side stray capacitance Cy2 Secondary side stray capacitance Rh Q-dump resistor Rs Earth resistance Vi input voltage Vo output voltage

Claims

1. A device formed by mounting circuit components on a printed wiring board having a plurality of wiring layers, the device converting an input voltage input between a primary power supply line and a primary ground line formed by a pair of wiring patterns into a predetermined output voltage and generating the output voltage between a secondary power supply line and a secondary ground line formed by a pair of wiring patterns, a primary side interphase capacitor element connected between the primary side power supply line and the primary side ground line, for substantially shorting the primary side power supply line and the primary side ground line in a frequency band equal to or higher than a switching frequency, thereby making the two lines into a primary side stable potential line that is stable in terms of potential; a secondary side interphase capacitor element connected between the secondary side power supply line and the secondary side ground line, for substantially shorting the secondary side power supply line and the secondary side ground line in a frequency band equal to or higher than the switching frequency, thereby making the two lines into a secondary side stable potential line that is stable in terms of potential; an inverter circuit including an isolation transformer and a switching element, a primary main winding of the isolation transformer and the switching element being connected in series, and the switching element being switched on and off at the switching frequency to generate a voltage that is an intermittent version of the input voltage across both ends of the primary main winding; a rectifier circuit connected to a secondary main winding of the isolation transformer, the rectifier circuit rectifying a voltage generated in the secondary main winding to generate a rectified voltage; a smoothing circuit including the secondary side interphase capacitor element, smoothing the rectified voltage to generate the output voltage across the secondary side interphase capacitor element; In an actual use state, the input voltage is supplied from an input power supply that is grounded to a ground line via a ground resistance, the primary side stabilized potential line and the ground line are connected by a primary side floating capacitance, the secondary side stabilized potential line and the ground line are connected by a secondary side floating capacitance, inter-winding floating capacitance is formed between the primary side main winding and the secondary side main winding, wiring patterns at locations in the inverter circuit, the rectifier circuit, and the smoothing circuit where a pulse voltage that oscillates at the switching frequency is generated are connected to the ground line by non-stable potential floating capacitance, In a switching power supply device in which a voltage generated in the primary main winding becomes a noise source, and a first noise current flows out to the ground line through the unstable potential floating capacitance, and a second noise current flows out to the ground line through the secondary floating capacitance, the isolation transformer has a secondary side auxiliary winding, one end of which is connected to the secondary side stable potential line, a wiring pattern connected to the other end of the secondary side auxiliary winding has a second main body region and a second capacitance forming region continuous therewith, the primary side stable potential line has a first main body region and a first capacitance forming region continuous therewith, the first and second capacitance forming regions face each other to form a wiring pattern stray capacitance, and the wiring pattern stray capacitance is set to a predetermined capacitance value by adjusting the facing areas of the first and second capacitance forming regions, A switching power supply device characterized in that, in the actual usage state, a current corresponding to the capacitance value flows through the wiring pattern stray capacitance, thereby suppressing the magnitude of the combined current of the first noise current and the second noise current to below a reference value.

2. 2. The switching power supply device according to claim 1, wherein a part or all of the secondary main winding and the secondary auxiliary winding are shared by each other.

3. A device formed by mounting circuit components on a printed wiring board having a plurality of wiring layers, the device converting an input voltage input between a primary power supply line and a primary ground line formed by a pair of wiring patterns into a predetermined output voltage and generating the output voltage between a secondary power supply line and a secondary ground line formed by a pair of wiring patterns, a primary side interphase capacitor element connected between the primary side power supply line and the primary side ground line, for substantially shorting the primary side power supply line and the primary side ground line in a frequency band equal to or higher than a switching frequency, thereby making the two lines into a primary side stable potential line that is stable in terms of potential; a secondary side interphase capacitor element connected between the secondary side power supply line and the secondary side ground line, for substantially shorting the secondary side power supply line and the secondary side ground line in a frequency band equal to or higher than the switching frequency, thereby making the two lines into a secondary side stable potential line that is stable in terms of potential; an inverter circuit including an isolation transformer and a switching element, a primary main winding of the isolation transformer and the switching element being connected in series, and the switching element being switched on and off at the switching frequency to generate a voltage that is an intermittent version of the input voltage across both ends of the primary main winding; a rectifier circuit connected to a secondary main winding of the isolation transformer, the rectifier circuit rectifying a voltage generated in the secondary main winding to generate a rectified voltage; a smoothing circuit including the secondary side interphase capacitor element, smoothing the rectified voltage to generate the output voltage across the secondary side interphase capacitor element; In an actual use state, the input voltage is supplied from an input power supply that is grounded to a ground line via a ground resistance, the primary side stabilized potential line and the ground line are connected by a primary side floating capacitance, the secondary side stabilized potential line and the ground line are connected by a secondary side floating capacitance, inter-winding floating capacitance is formed between the primary side main winding and the secondary side main winding, wiring patterns at locations in the inverter circuit, the rectifier circuit, and the smoothing circuit where a pulse voltage that oscillates at the switching frequency is generated are connected to the ground line by non-stable potential floating capacitance, In a switching power supply device in which a voltage generated in the primary main winding becomes a noise source, and a first noise current flows out to the ground line through the unstable potential floating capacitance, and a second noise current flows out to the ground line through the secondary floating capacitance, the isolation transformer has a primary side auxiliary winding, one end of which is connected to the primary side stable potential line, a wiring pattern connected to the other end of the primary side auxiliary winding has a first main body region and a first capacitance forming region continuous therewith, the secondary side stable potential line has a second main body region and a second capacitance forming region continuous therewith, the first and second capacitance forming regions face each other to form a wiring pattern stray capacitance, and the wiring pattern stray capacitance is set to a predetermined capacitance value by adjusting the facing areas of the first and second capacitance forming regions, A switching power supply device characterized in that, in the actual usage state, a current corresponding to the capacitance value flows through the wiring pattern stray capacitance, thereby suppressing the magnitude of the combined current of the first noise current and the second noise current to below a reference value.

4. 4. The switching power supply device according to claim 3, wherein a part or all of the primary main winding and the primary auxiliary winding are shared by each other.

5. 5. A switching power supply device as claimed in claim 1, further comprising a coupling capacitor element connected between the primary side stable potential line and the secondary side stable potential line, and which substantially shorts the primary side stable potential line and the secondary side stable potential line in a frequency band equal to or higher than a switching frequency.

6. a Q damping resistor element is inserted in series in at least one of a boundary between the first body region and the first capacitance forming region and a boundary between the second body region and the second capacitance forming region; 5. The switching power supply device according to claim 1, wherein the sharpness of resonance occurring in a frequency band higher than the switching frequency of a resonance system formed by the inter-winding stray capacitance, the wiring pattern stray capacitance, and a parasitic inductance component existing in the vicinity of these is suppressed by the Q damping resistor element.

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